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The hydration reactions of calcium aluminate cements are very complex. The strength-developing phases are monocalcium aluminate (CA), dodeca-calcium hepta-aluminate (C 12 A 7), and belite (C 2 S), a dicalcium silicate. Calcium aluminoferrite (C 4 AF), monocalcium dialuminate (CA 2), gehlenite, and pleochroite contribute little to the concrete ...
The necessary additional calcium is provided by the calcium hydroxide and calcium silicate hydrate in the cement paste; The effect of these changes is an overall loss of concrete strength. The above effects are typical of attack by solutions of sodium sulfate or potassium sulfate. Solutions containing magnesium sulfate are generally more ...
Calcium aluminates can form complex salts in combination with different types of anions.Two series of calcium aluminates are known in cement chemistry: AFm and AFt phases, being respectively mono- or tri-substituted with a given divalent anion X (e.g. SO 2− 4, CO 2− 3, or hosting a divalent impurity such as SeO 2− 4 [3]...), or with two units of a monovalent anion, e.g. OH −, Cl − ...
Calcium aluminates phase diagram Crystal structure of dodecacalcium hepta-aluminate, 12CaO·7Al 2 O 3 (C 12 A 7). [1] Calcium aluminates are a range of materials [2] obtained by heating calcium oxide and aluminium oxide together at high temperatures. They are encountered in the manufacture of refractories and cements.
Calcium aluminate cements are hydraulic cements made primarily from limestone and bauxite. The active ingredients are monocalcium aluminate CaAl 2 O 4 (CaO · Al 2 O 3 or CA in cement chemist notation, CCN) and mayenite Ca 12 Al 14 O 33 (12 CaO · 7 Al 2 O 3, or C 12 A 7 in CCN). Strength forms by hydration to calcium aluminate hydrates.
AFm form inter alia when tricalcium aluminate 3CaO·Al 2 O 3, or C 3 A in CCN, reacts with dissolved calcium sulfate (CaSO 4), or calcium carbonate (CaCO 3). As the sulfate form is the dominant one in AFm phases in the hardened cement paste (HCP) in concrete, AFm is often simply referred to as Aluminate Ferrite monosulfate or calcium aluminate ...
In calcium aluminate cements, it exists as a solid solution in which the amount of minor elements depends upon the bulk composition of the cement. A typical composition [4] is Ca 0.93 Al 1.94 Fe 0.11 Si 0.02 O 4.
It represents a group of calcium aluminate hydrates. AFt has the general formula [Ca 3 (Al,Fe)(OH) 6 •12H 2 O] 2 •X 3 •nH 2 O where X represents a doubly charged anion or, sometimes, two singly charged anions. Ettringite is the most common and prominent member of the AFt group (X in this case denoting sulfate), and often simply called ...